feat: add Hunk notify stream

[benvinegar]

Summary

• add a loopback SSE notify stream at /notify that emits typed Hunk session events
• store focused and published hunk selections in the daemon and expose them through hunk session selection ...
• mirror the UI focus into daemon selection state and publish the current selection when p is used

Notes

• this is a stacked PR on top of feat: export selected hunk to pi #73
• the intended architecture is: notify stream for events, local hunk session ... CLI for state reads
• the Pi file bridge remains as a compatibility/prototype adapter for now

Testing

• bun run typecheck
• bun test test/cli.test.ts test/session-commands.test.ts test/mcp-daemon.test.ts test/mcp-server.test.ts test/pi-selection.test.ts test/app-interactions.test.tsx